1. Field of the Invention:
This invention relates to steam turbine power plants, and in particular, to a steam turbine power plant having a pressure-increasing device inserted between a steam supply source and a drive turbine element of the power plant. 2. Description of the Prior Art:
In general, steam power plants comprise a high pressure, high temperature steam generator element supplying motive fluid to a closed loop arrangement of one or more steam turbines and associated apparatus. One of the most elemental closed loop arrangements is that comprising a high pressure turbine, an intermediate pressure turbine, and a low pressure turbine having a condenser attached thereto, connected in series with the steam generator. The high pressure, high temperature steam produced by the steam generator element is permitted to expand through each of the turbine elements and is collected and returned to the liquid state in the condenser element. From the condenser element, the condensate is conducted through a series of feed pumps and feedwater heaters before it is reintroduced into the steam generator to complete the closed system.
Although the elements described above are found in virtually all of the steam power plants utilized for the generation of electrical power, it is well known to those skilled in the art that numerous other associated apparatus, such as boiler feed pumps or fans, are interconnected with the basic system above described.
It is also well known to those skilled in the art that steam power plants for the generation of electrical power commonly utilize steam driven turbines to provide a source of power for the associated apparatus. Most commonly, the steam supply source for the drive turbine is taken either from the high pressure turbine exhaust or from the exhaust of the intermediate pressure turbine element. However, a source of steam to supply a drive turbine element may be found at a predetermined extraction point within the low pressure turbine element.
The drive turbine for the associated apparatus is generally designed for maximum efficiency when the overall power plant is operating at its maximum calculated load. As the overall steam power plant load is reduced, for example, during those periods when peak power output is not required, the steam supply pressure to the drive turbine elements decreases in direct proportion to the decrease in the overall power plant load.
However, it is common to find that the power requirements of the associated apparatus do not decrease commensurately with the decrease in drive steam supply. Thus, the drive turbines are required to produce a proportionally greater power output in order to adequately power the associated apparatus at a time when the steam supply source to the drive turbines is decreasing. For example, at about 40% of the overall steam power plant maximum guaranteed load, the nozzle of the drive turbine for the associated plant apparatus is unable to pass sufficient steam flow in order to power the associated apparatus.
If the drive turbine has only a single steam chest, prior art has switched the drive turbine steam supply source to a higher pressure zone in order to meet the increased power requirements impressed upon the drive turbine by the associated plant apparatus. Such higher pressure zones utilized by the prior art for supplying the drive turbine elements include a cold reheater element of the overall system or the high pressure, high temperature throttle steam. If the drive turbine has a dual steam chest, the prior art admits high pressure steam from either of the chosen sources into the high pressure steam chest. In both cases however, the high pressure steam is throttled severely upon introduction into the drive turbine element, with a concomitant loss in available energy.